Ion guide

ABSTRACT

An ion guide may comprise a set of plate electrodes, each plate electrode having a plurality of apertures formed therethrough. The set of plate electrodes are spatially arranged such that a relative positioning of each plurality of apertures of a respective plate electrode of the set of plate electrodes and respective adjacent plate electrodes of the set of plate electrodes defines a continuous ion flight path through the respective plurality of apertures of each plate electrode of the set of plate electrodes. The continuous ion flight path has a helical-based and/or spiral-based shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation under 35 U.S.C. § 120 andclaims the priority benefit of co-pending U.S. patent application Ser.No. 16/413,463, filed May 15, 2019. The disclosure of the foregoingapplication is incorporated herein by reference.

TECHNICAL FIELD OF THE DISCLOSURE

The disclosure concerns ion guides, especially for use in an ionmobility spectrometer or a mass spectrometer.

BACKGROUND TO THE DISCLOSURE

Ion guides are used in a variety of applications, in both massspectrometry and ion mobility spectrometry (IMS). In IMS, ions arepushed down a gas filled drift tube by an electric field and separatespatially according to their ion mobilities. The resolution of an IMSdevice increases with the length of the drift region, but very longdevices are unsuited to commercial instrumentation, due to their size.It is therefore advantageous to fold the drift path into a more compactstructure, conceptually similar to multi-turn time-of-flight massspectrometers. The use of IMS in a mass spectrometer is described inPatent Publication No. 2004/031920, for example.

US Patent Publication No. 2011/0168882 discusses an ion guide or ionmobility spectrometer having a helical, toroidal, part-toroidal,hemitoroidal, semitoroidal or spiral ion guiding region. The ion guidecomprises a plurality of stacked electrodes each having an aperturethrough which ions are transmitted. A RF voltage is applied to theelectrodes in order to confine ions radially within the ion guide. A DCor transient DC voltage is applied to at least some of the electrodes inorder to urge ions along the ion guide. The number of electrodesrequired for such a design is proportional to the length of the ionguide. This is consequently a difficult and expensive design tomanufacture and could have a high chance of electrical failure, due tothe large number of electrical connections required.

US Patent Publication 2014/0353487 describes a different IMS method thatsends ions multiple times around a closed loop. This is space-efficient,but has a low duty cycle and limitations in its ion mobility range orresolution, as higher ion mobility ions could eventually catch up withlower ion mobility ions in the closed loop.

US Patent Publication 2014/0042315 relates to measuring ion mobility ingases at pressures of a few hectopascal. Drift regions are bent intocurved shapes, which extend into a third dimension. Alternatingdirections of curvature in the curved shapes (that is, both clockwiseand anticlockwise curvature) balance out different path lengths bypassing through approximately equal drift distances on outer and innertrajectories. The different path lengths would otherwise result in aloss of resolution. Ions are held near the axis of the curved driftregion by sectional or permanent focusing, so that the average driftpath is constant. One possible shape is a double loop in the shape of afigure eight. The shape extends perpendicular to its plane ofprojection, so that several double loops lie on top of each other.Whilst such an arrangement may have its advantages, it is still complexto manufacture. Moreover, it would be expected that ions move back andforth between inner and outer edges as they travel, so the practicalimpact of this design might be less than originally envisaged.

Japanese Patent Publication 2007/311111 describes a Time-of-Flight (TOF)mass spectrometer formed using an inner metal plate and an outer metalplate, which define a spiral ion flight path. A shunt is providedbetween the inner metal plate and the outer metal plate to prevent beaminteractions. This arrangement is also described in “A New SpiralTime-of-Flight Mass Spectrometer for High Mass Analysis”, Satoh et al,J. Mass Spectrom. Soc. Jpn. Vol. 54, No. 1, 2006.

Ion guide designs, suitable for use in IMS, which are morestraightforward to manufacture, more robust and can provide highresolution performance are therefore desirable.

SUMMARY OF THE INVENTION

There is provided: ion guides in accordance with claims 1 to 42; an ionmobility spectrometer in line with claim 43; and a mass spectrometer inaccordance with claim 44. Further features of the invention are detailedin dependent claims and discussed herein.

An ion guide in a first aspect comprises a set of electrodes, which areeach a plate electrode or an electrode structure that functionallymimics a plate electrode (at least one example of which will bediscussed below). For simplicity, the term “plate electrode” will beused to cover all such electrode structures. Multiple apertures areformed through each of the plate electrodes. The set of plate electrodes(each having a plurality of apertures) are spatially arranged (ormounted) such that a relative positioning of the plurality of aperturesof each plate electrode and the apertures of its adjacent plateelectrodes defines a continuous ion flight path through the multipleapertures of each of the set of plate electrode.

A single continuous ion flight path may thereby be provided through themultiple apertures of each of the set of plate electrode. It ispreferred that the plate electrodes are arranged consecutively, that isin a stack, such that an n^(th) plate electrode is adjacent to an(n+1)^(th) plate electrode, where n=1 to N−1, wherein N is the totalnumber of plate electrodes. Further preferably, the N^(th) plateelectrode is adjacent to the first (n=1) plate electrode, that is suchthat the last electrode (N^(th)) meets the first electrode. Thereby theplate electrodes are arranged in a curved stack. The number of plateelectrodes may be as few as 30 and as high as 180.

In some embodiments, at least some of the set of plate electrodes arespatially arranged around an axis that extends in an axial dimension,for example in a circle or circular arrangement around the axis,although other arrangements are possible as described below, such asoval, rounded rectangular, or labyrinthine. In this way, the continuousion flight path rotates around the axis that extends in the axialdimension. The axis thus becomes an axis of rotation for the ion flightpath. In this way, the continuous ion flight path has a spiral,spiral-like, helical or helical-like shape (or a combination thereof),as described further below. Where a spiral, spiral-like or spiral-basedshape is discussed, this may refer to a shape having a fundamentalspiral character, for instance a curve with a generally increasing (ordecreasing) radius from a central point or line. A helical, helical-likeor helical-based shape may refer to a shape having a fundamental helicalcharacter, for instance a curve extending along an axis and having agenerally repeating shape. These terms will be further discussed below.

Preferably, each plate electrode of the set of plate electrodes has therespective plurality of apertures spaced apart along a first dimension.In some embodiments, the first dimension is the same as the axialdimension (that is, generally parallel with the axis). By such anarrangement, the continuous ion flight path has a helical character. Inother embodiments, the first dimension is perpendicular to the axialdimension. Then, the continuous ion flight path has a spiral character(although it may also have a helical character, as will be discussedfurther). The apertures are spaced apart along the first dimension by anaperture spacing. Preferably, each electrode has the same spacing ofapertures along the first dimension. Further preferably, a respectiveplate electrode of the set of plate electrodes has its respectiveplurality of apertures positioned so as to be offset in the firstdimension from the respective plurality of apertures of a respectiveadjacent plate electrode. Where the first dimension is perpendicular tothe axial dimension (such that a spiral continuous ion flight path isformed), the offset may be in both the first dimension and the axialdimension. Then, the continuous ion flight path has both a spiral andhelical character.

To achieve this, in some embodiments, the respective adjacent plateelectrodes of the set of plate electrodes are positioned so as to beoffset from one another in the first dimension, especially wherein theplate electrodes are substantially identical. In some other embodiments,less preferred from a manufacturing perspective, an offset of theapertures may be defined by a variation in the position of the apertureson each plate electrode.

The offset is preferably less than the aperture spacing. In this way,the continuous ion flight path extends slightly (that is, less than theaperture spacing within each electrode) in the first dimension as itpasses from a respective plate electrode to a respective adjacent plateelectrode. Preferably, for a full rotation of the continuous ion flightpath, that is, after passing through each plate electrode, the ionflight path extends in the first dimension by an amount equal to theaperture spacing. This is preferable for example, in the embodimentswhere the last electrode (N^(th)) meets the first electrode.Accordingly, it is preferred that the offset is substantially equal toy/N, where y is the aperture spacing within each plate electrode and Nis the number of plate electrodes. Thus, in some preferred embodiments,after the continuous ion flight path has passed through every respectivefirst aperture of each plate electrode, the continuous ion flight pathcommences to pass through a respective second aperture of each plateelectrode, thereafter optionally through a respective third aperture ofeach plate electrode and so on. Generally, where the plate electrodeseach have x apertures (x is at least 2, preferably 2 to 100, morepreferably 3 to 100), the continuous ion flight path will pass x timesthrough each plate electrode, passing through the apertures of eachplate electrode in sequence.

In contrast with known ion guide structures, this design can providehigh IMS resolution in a reasonably compact device, but requires manyfewer electrodes (and other components) and electrical connections toachieve a flight path of the same length, since different parts(apertures) of each electrode provide different portions of a singleflight path. The difference may be an order of magnitude. Between 5 and100 apertures per electrode may be provided, in embodiments. Using fewerelectrodes makes the structure more electrically robust and easesmanufacture, reducing cost. Accuracy may also be improved. In comparisonwith closed-loop flight path designs, a higher duty cycle can beachieved. In closed-loop ion guide structures (such as US-2014/0353487),it is possible for some ions to complete more cycles of the closed-loopflight path than others. This disadvantage is not present in embodimentsof the present disclosure, providing a greater ion mobility range thatis preserved at high resolution.

Where the ion flight path has a helical shape, this is not necessarilyhelical in a mathematical sense. The helical shape is thus intended tomean helical-like, which includes helical, substantially helical orother shapes having an aspect of helical character, examples of whichare described herein. Similarly, a spiral shape is not necessarilyspiral in a mathematical sense and may mean spiral-like, which includessubstantially spiral or other shapes having an aspect of spiralcharacter, examples of which are described herein. A wide variety ofspiral-like and helical-like shapes for the ion flight path are possiblewith this design. The helical shape can define a two-dimensional profileand typically, the defined ion flight path extends multiple times alongthe two-dimensional profile as it extends in the first dimension, whichis generally perpendicular to the two-dimensional profile. Thetwo-dimensional profile may be circular, oval, rounded rectangular,labyrinthine or figure-of-eight, for instance. A figure-of-eight twodimensional profile (or more generally, one with both clockwise andanticlockwise curvature) may be provided using first and secondpluralities of electrodes, each of which is arranged to define acircular two-dimensional profile. Thus, the first plurality ofelectrodes may be arranged around a first axis and the second pluralityof electrodes may be arranged around a second axis, wherein both firstand second axes extend in the first dimension along which the pluralityof apertures of each plate electrode are spaced apart. Some of the firstplurality of electrodes and some of the second plurality of electrodesare arranged to interleave with one another, such that thetwo-dimensional profile of the first plurality of electrodes overlapswith the two-dimensional profile of the second plurality of electrodes.Then, the continuous ion flight path can be defined by the apertures ofboth the first and second pluralities of electrodes. The interleavingelectrodes may be provided with alternating parts with an aperture andgaps (or notches), such that the part with an aperture of one of thefirst plurality of electrodes fits into the gap part of a correspondingone of the second plurality of electrodes (and vice versa).

Each plate electrode may have one or more of the same: shape; size; andpositioning and/or spacing of apertures. Where identical plateelectrodes are used, they are typically offset from each other along theaxis of the helical shape. The offset between one plate electrode and anadjacent plate electrode is preferably less than the spacing ofapertures within a plate electrode. The offset between one plateelectrode and an adjacent plate electrode is thus preferably arrangedsuch that after each complete rotation, the p^(th) aperture of the lastelectrode (N^(th)) is adjacent the (p+1)^(th) aperture of the firstelectrode in the sequence (1≤p<x−1, where x is the number of aperturesin each electrode). In some embodiments, each of the apertures of eachplate electrode has a rectangular or ovoid shape. It is not necessaryfor all of the apertures to have the same shape or arrangement anddesigns utilising this approach will be discussed with reference to anion guide of a second aspect, below.

For radial ion confinement, an RF power supply may provide each plateelectrode with a respective RF voltage, especially such that adjacentelectrodes receive RF voltages with different phases. In particular, afirst RF voltage may be applied to every second plate electrode asspatially arranged and to provide a second RF voltage (having oppositephase to the first RF voltage) to every second plate electrode of theset of electrodes not receiving the first RF voltage. A DC power supplymay supply at least one DC potential to one or more electrodes of theset of electrodes, particularly to form a travelling wave, so as tocause ions to travel through the defined ion flight path.

Each RF voltage may have an amplitude selected from: (i) <100 V peak topeak; (ii) 100-200 V peak to peak; (iii) 200-300 V peak to peak; (iv)300-400 V peak to peak; (v) 400-500 V peak to peak; and (vi) >500 V peakto peak. Each RF voltage may have a frequency selected from: (i) <100kHz; (ii) 100-500 kHz; (iii) 0.5-1.0 MHz; (iv) 1.0-1.5 MHz; (v) 1.5-2.0MHz; (vi) 2.0-2.5 MHz; (vii) 2.5-3.0 MHz; (viii) 3.0-4.0 MHz; (ix)4.0-5.0 MHz; (x) 5.0-6.0 MHz; (xi) 6.0-7.0 MHz; (xii) 7.0-8.0 MHz;(xiii) 8.0-9.0 MHz; (xiv) 9.0-10.0 MHz; and (xv) >10.0 MHz. The DCtravelling wave voltages or waveforms are preferably translated alongthe set of electrodes of the ion guide at a velocity selected from: (i)<100 m/s; (ii) 100-500 m/s; (iii) 500-1000 m/s; (iv) 1000-1500 m/s; (v)1500-2000 m/s; (vi) 2000-2500 m/s; (vii) 2500-3000 m/s; (viii) >3000m/s.

A mounting element, on which the set of electrodes are mounted, may beprovided in order to set the relative positioning of apertures betweenadjacent electrodes of the set of electrodes. The mounting element (forexample, a printed circuit board) may comprise one or more electricalconnections to the set of electrodes.

In some embodiments, the mounting element comprises: a first mountingsubstrate, to which a first end of each electrode of the set ofelectrodes is attached; and a second mounting substrate (opposite thefirst mounting substrate), to which a second end of each electrode ofthe set of electrodes is attached. The first and second mountingsubstrates may thereby be spaced apart from each other along the firstdimension, that is, the direction in which the apertures are spacedapart within each plate electrode, with the plate electrodes sandwichedbetween. The first mounting substrate may comprise one or more firstelectrical connections to every second plate electrode of the set ofelectrodes as spatially arranged. The second mounting substrate maycomprise one or more second electrical connections to every second plateelectrode of the set of electrodes between the electrodes connected tothe one or more first electrical connections. The second electricalconnections may be arranged to provide an electrical power that isdifferent from an electrical power provided by the first electricalconnections, for example the first and second RF voltages and/or the atleast one DC potential described above. The first and second mountingsubstrates may each comprise a printed circuit board (PCB), which isconvenient for providing the electrical connections. Furthermore, thePCB is preferably flexible enough to be bent into a desired shape. Insome embodiments, the PCB may comprise a substantially helical form. Insuch embodiments, preferably the PCB comprises a ring shape having a cutin which the two ends of the PCB adjacent the cut are spaced apart. Theends may be spaced apart by a distance that is substantially equal tothe aperture spacing within each plate electrode. A spacer may beprovided between the cut ends of the PCB for this purpose.

The mounting element may comprise a mounting substrate. In certainembodiments, each electrode of the set of electrodes is attached to themounting substrate, which has a shape to thereby set the relativepositioning of apertures between adjacent electrodes of the set ofelectrodes. In other embodiments, the mounting element further comprisesa spacer, positioned between the mounting substrate and the set ofelectrodes. The spacer may be configured to set the relative positioningof apertures between adjacent electrodes of the set of electrodes.

An ion guide of a second aspect comprises a plurality of electrodes,each electrode comprising at least one aperture, so as to define an ionflight path (preferably curved). This aspect may be combined with thefirst aspect, in which case, each electrode may be a plate electrode (ora structure functionally mimicking a plate electrode), having multipleapertures and the ion flight path may have a helical shape. In thissecond aspect, an aperture of a first electrode is advantageouslyadjacent to an aperture of a second electrode along the ion flight path.The aperture of the second electrode has a shape, electric potentialand/or position different from that of the aperture of the firstelectrode so as to cause ions travelling along the ion flight path toshift in a direction perpendicular to the direction of the ion flightpath. Advantageously, the ion flight path has at least one curve. Inthis approach, the ions may be caused to travel along different parts ofthe curvature of the same path, which may mitigate path lengthdifference effects. This should reduce resolution loss (or increase anylimit on resolution) in comparison with wider apertures or smallerhelical radii, allowing good resolution on smaller devices or deviceswith higher space charge capacity. In another sense, it may beconsidered that the at least one curve defines an average radius ofcurvature. Then, the ions may be caused to oscillate between inside theaverage radius of curvature and outside the average radius of curvature.As a consequence, a difference in flight path length between ionsentering the ion guide at a position inside the average radius ofcurvature and ions entering the ion guide at a position outside theaverage radius of curvature may be corrected.

Beneficially, the direction perpendicular to the direction of the ionflight path may defined by a (further) helical shape, the direction ofthe ion flight path being an axis of the (further) helical shape. In thecombination of the first and second aspects, the ions may thereby travelalong a helical path that is perpendicular to the helical shape.

One way to provide this effect is by each of the aperture of the firstelectrode and the aperture of the second electrode comprising arespective first slot and a respective second slot, each first slotbeing distinct and separated from the respective second slot. The firstslot of the aperture of the second electrode may have a shape and/orposition different from the first slot of the aperture of the firstelectrode, so as to cause ions travelling along the ion flight path toshift in a first direction perpendicular to the direction of the ionflight path. Additionally (and less preferably, alternatively), thesecond slot of the aperture of the second electrode has a shape and/orposition different from the second slot of the aperture of the firstelectrode, so as to cause ions travelling along the ion flight path toshift in a second direction perpendicular to the direction of the ionflight path. The first and second directions are typically the same in arotational sense (for example, both clockwise or both anti-clockwise).Each first slot and each second slot may have a shape defined byrespective portions of the same rectangle.

A third aspect of an ion guide (which can again be combined with eitheror both of the first and second aspects), comprises: a first pluralityof electrode arrangements, each electrode arrangement comprisingrespective parallel bar electrodes, with a respective gap therebetween;and a second plurality of electrode arrangements, each electrodearrangement comprising respective parallel electrode parts, with arespective gap therebetween. The parallel electrode parts of the secondplurality of electrode arrangements are arranged orthogonally withrespect to the parallel bar electrodes of the first plurality ofelectrode arrangements (for example, with the bar electrodes beingarranged horizontally and the parallel electrode parts of the secondplurality of electrode arrangements being arranged vertically). This maybe effected such that the respective gaps of the first plurality ofelectrode arrangements are aligned with the respective gaps of thesecond plurality of electrode arrangements to allow ions to traveltherethrough along a continuous path. The first and second pluralitiesof electrode arrangements are arranged alternately along the continuouspath (that is, spaced apart with each first electrode arrangement beingdirectly followed by a second electrode arrangement and each secondelectrode arrangement being directly followed by a first electrodearrangement, with the exception of the last electrode arrangement in theion guide). Each of the first plurality of electrode arrangements (andoptionally, each of the second plurality of electrode arrangements) istherefore not strictly a plate electrode, but rather an electrodestructure that mimics a plate electrode using bar electrodes. Successiveelectrode arrangements in the first plurality of electrode arrangements(or in the second plurality of electrode arrangements) are preferablyprovided with RF potentials of different (optionally, opposite) phase.Such a structure may be a form of plate electrode used in ion guidesaccording to the first aspect.

In certain embodiments, each of the first plurality of electrodearrangements are provided with (only) an RF potential and each of thesecond plurality of electrode arrangements are provided with (only) a DCpotential. The potentials can be applied to the first and secondpluralities of electrode arrangements in a similar manner to embodimentsof the aspects described above. For example, a first RF voltage may beapplied to every second electrode arrangement of the first plurality ofelectrode arrangements and a second RF voltage (preferably havingopposite phase to the first RF voltage) to every second electrodearrangement of the first plurality of electrode arrangements notreceiving the first RF voltage. A DC power supply may supply the DCpotential to each of the second plurality of electrode arrangements,preferably to form a travelling wave, so as to cause ions to travelthrough the defined ion flight path.

Each RF voltage may have an amplitude selected from: (i) <100 V peak topeak; (ii) 100-200 V peak to peak; (iii) 200-300 V peak to peak; (iv)300-400 V peak to peak; (v) 400-500 V peak to peak; and (vi) >500 V peakto peak. Each RF voltage may have a frequency selected from: (i) <100kHz; (ii) 100-500 kHz; (iii) 0.5-1.0 MHz; (iv) 1.0-1.5 MHz; (v) 1.5-2.0MHz; (vi) 2.0-2.5 MHz; (vii) 2.5-3.0 MHz; (viii) 3.0-4.0 MHz; (ix)4.0-5.0 MHz; (x) 5.0-6.0 MHz; (xi) 6.0-7.0 MHz; (xii) 7.0-8.0 MHz;(xiii) 8.0-9.0 MHz; (xiv) 9.0-10.0 MHz; and (xv) >10.0 MHz. The DCtravelling wave voltages or waveforms are preferably translated alongthe set of electrodes of the ion guide at a velocity selected from: (i)<100 m/s; (ii) 100-500 m/s; (iii) 500-1000 m/s; (iv) 1000-1500 m/s; (v)1500-2000 m/s; (vi) 2000-2500 m/s; (vii) 2500-3000 m/s; (viii) >3000m/s.

Optionally, the second plurality of electrode arrangements couldcomprise plate electrodes, each having an aperture to provide therespective gap.

Other aspects of the disclosure include an ion mobility spectrometer ora mass spectrometer, comprising the ion guide of any aspect. In the ionmobility spectrometer, the ion guide is advantageously configured as adrift tube. In the mass spectrometer, the ion guide may be configured toreceive ions from an upstream ion source or ion optical device and tocause the received ions to travel along the ion flight path. The massspectrometer may further comprise a mass analyser, configured to receiveions that have travelled along the ion flight path. Optionally, an ionoptical bypass arrangement may be provided, configured selectively tocause ions to travel from the upstream ion source or ion optical deviceto the mass analyser without passing through the ion guide.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be put into practice in a number of ways, andpreferred embodiments will now be described by way of example only andwith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a first design of an ion guide inaccordance with the disclosure;

FIG. 2 shows a manufacture step of a mounting substrate according to afirst design, for the ion guide of FIG. 1 ;

FIGS. 3A, 3B, 3C and 3D show manufacture steps for forming an ion guidein accordance with the design of FIG. 1 ;

FIG. 4 schematically depicts an operation of an ion guide in accordancewith the design of FIG. 1 ;

FIG. 5 is a schematic diagram showing connections to and interfaces withan ion guide in accordance with the design of FIG. 1 , for operation;

FIG. 6 schematically illustrates a mass spectrometer comprising an ionguide in accordance with the design of FIG. 1 ;

FIG. 7A depicts an example electrode structure and mounting substrateaccording to a second design of an ion guide in accordance with thedisclosure;

FIG. 7B depicts an example electrode structure and mounting substrateaccording to a third design of an ion guide in accordance with thedisclosure;

FIGS. 8A and 8B schematically show variant profiles for ion guides inaccordance with the disclosure;

FIG. 9 depicts schematically an electrode structure and profile of afourth design of an ion guide in accordance with the disclosure;

FIG. 10A shows a top view of a fifth design of an ion guide inaccordance with the disclosure;

FIG. 10B shows a top view of a first part of a variant on the design ofFIG. 10A;

FIG. 10C shows a top view of a second part of the design of FIG. 10B;

FIG. 10D schematically illustrates an ion flight path for the design ofFIGS. 10B and 10C;

FIG. 11A illustrates a first example of electrode aperture shapes inaccordance with the disclosure, suitable for ion guides;

FIG. 11B illustrates a second example of electrode aperture shapes inaccordance with the disclosure, suitable for ion guides; and

FIG. 12 is a perspective view of a sixth design of an ion guide inaccordance with the disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A number of different ion guide designs, structures and associatedmanufacturing methods are described below. Although certain features aredescribed with reference to one or more particular embodiments ordesigns, it will be understood that these can also be applied to otherembodiments or designs disclosed herein, wherever possible. Where thesame parts are shown in different drawings, identical reference numeralshave been used, for clarity.

Referring first to FIG. 1 , there is shown a perspective view of a firstdesign of an ion guide 10 in accordance with the disclosure. The ionguide 10 comprises: a first mounting printed circuit board (PCB) 20; asecond mounting PCB 30; and a plurality of plate electrodes 40. Each ofthe plate electrodes 40 is mounted between the first mounting PCB 20 andthe second mounting PCB 30 (in a sandwich structure). The number ofelectrodes may be limited at a lower bound by the radius becoming tooconstricted to fit in plates (in particular, solid plates) or when thecurvature between each plate becomes disruptive to the field. The upperlimit on the number may be complexity and capacitance, as much as space.Between 30 and 180 plates may therefore be possible, dependent on theradius of curvature and size of the electrodes. Moreover, each of theplate electrodes 40 has a plurality of apertures; all of the plateelectrodes 40 have the same size, shape and aperture arrangement. Inprinciple, the number of apertures per plate electrode 40 could be assmall as two and it could be as high as 100 (or potentially greater).

The resultant ion guide 10 can thereby more generally be seen tocomprise a curved stack (in this case circular) of elongated electrodes40, each mounted to PCB mounting substrates 20, 30 and incorporating anarray of apertures so that the stack defines a series of channels. Asmall axial shift from one electrode to the next due to the shape of thefirst 20 and second 30 mounting PCBs (or alternatively in the positionsof the apertures themselves) causes the channels between apertures tooverlap and merge into a fused, elongated 3D ion path. The ion path hasa helical shape.

In general terms, there may therefore be considered a first aspect of anion guide. The ion guide comprises a set of plate electrodes (orelectrodes that are each configured to mimic a plate electrodefunctionally). Each plate electrode has a plurality of apertures formedtherethrough. The set of plate electrodes are spatially arranged (ormounted) such that a relative positioning of each plurality of aperturesof a respective plate electrode of the set of plate electrodes andrespective adjacent plate electrodes of the set of plate electrodesdefines a continuous ion flight path through the respective plurality ofapertures of each plate electrode of the set of plate electrodes. Thecontinuous ion flight path advantageously has a helical-based and/orspiral-based shape (the spiral-based shape will be discussed furtherlater in this disclosure, with reference to FIGS. 10A to 10D). Thecontinuous ion flight path may be considered a single ion flight path,although in practice, the continuous ion flight path may be divided intomultiple ion flight paths (at least one way of achieving this will bedescribed below). In a further aspect of the disclosure, there may beconsidered an ion mobility spectrometer, comprising any ion guide asdescribed herein, configured as a drift tube.

The set of plate electrodes may be considered as arranged in a sequence.Then, a first electrode in the sequence may be arranged to provide anaccess aperture for ions to enter the continuous ion flight path.Additionally or alternatively, a last electrode in the sequence may bearranged to provide an exit aperture for ions to leave the continuousion flight path. Typically, the number of plate electrodes may be as lowas 30 and/or as high as 180. For each plate electrode, the respectiveplurality of apertures comprises at least 3, 5, 10, 20, 30, 50, 70 or 80apertures and/or preferably no more than 80, 100 or 120 apertures.

Beneficially, each plate electrode of the set of plate electrodes hasthe respective plurality of apertures spaced apart along a firstdimension (which in some embodiments is the axis of the helical-basedshape). Then, the relative positioning of each plurality of aperturesmay define the continuous ion flight path to extend in the firstdimension. The relative positioning of each plurality of apertures maydefine the continuous ion flight path to extend in the first dimension.Some or all of the set of plate electrodes may be spatially arrangedaround an axis that extends in the first dimension. Then, the continuousion flight path typically has a helical-based shape. The first dimensionmay define an axis of the ion guide in such cases.

The relative positioning of each plurality of apertures of a respectiveplate electrode of the set of plate electrodes and respective adjacentplate electrodes of the set of plate electrodes preferably includesspacing along the first dimension. In other words, respective adjacentplate electrodes of the set of plate electrodes are positioned so as tobe offset from one another in the first dimension. This is oneimplementation of what is sometimes referred to as an axial shift inthis disclosure. Typically, in such embodiments, each electrode of theset of electrodes has the same spacing of apertures along the firstdimension. Then, the offset between the respective plurality ofapertures of one plate electrode of the set of plate electrodes and therespective plurality of apertures of one adjacent plate electrode of theset of plate electrodes is beneficially less than the spacing ofapertures. For instance, the offset between respective pluralities ofapertures of respective adjacent plate electrodes may be substantiallyequal to y/N, where y is the aperture spacing within each plateelectrode and N is the number of plate electrodes. Then, an offsetbetween one plate electrode of the set of plate electrodes (which may betermed a last of the set of plate electrodes arranged in a sequence) andone adjacent plate electrode of the set of plate electrodes (which maybe termed as a first of the set of plate electrodes in the sequence) isadvantageously substantially equal to the spacing of apertures (that isy).

Further optional, preferable and advantageous features of thisgeneralised aspect, also applying to its specific embodiments, will bediscussed below. Firstly, manufacturing details of the design accordingto this aspect will be detailed.

Now referring to FIG. 2 , there is shown a manufacture step of amounting substrate, for the ion guide of FIG. 1 . For simplicity, thefirst mounting PCB 20 is shown, but it will be understood that thistechnique is also applicable to the second mounting PCB 30. The PCB 20is initially a ring, which is cut at 21 and then bent or pushed 22 tocreate a helical form, with the gap 23 between the cut (terminal) endsof the PCB being flexed to a specific size. Provided that the PCB 20 issufficiently flexible, the helical form can be a single rotation andwith a fixed shape, by mounting the back of the PCBs to a plateincorporating this axial shift, or placing a spacer between the cut endsof each PCB 20, 30.

The axial shift over the rotation of the PCB 20, 30 (in other words, thehelical form of the PCB as shown in FIG. 2 ) induces the same axialshift in the stacked ring of electrodes 40 forming the ion guide 10. Asa result, if this axial shift corresponds to the spacing of theapertures within each electrode along the first dimension, the aperturesmerge to form a single fused helical ion channel with an inlet aperture42 and an outlet aperture 44.

In terms of the generalised aspect of the ion guide discussed above, theion guide may further comprise a mounting element, on which the set ofelectrodes are mounted in order to set the relative positioning ofapertures between adjacent electrodes of the set of electrodes. Themounting element may comprise a plurality of component parts in anintegral or separable structure. Advantageously, the mounting elementcomprises one or more electrical connections to the set of electrodes.The mounting element may comprise one or more PCBs.

In one embodiment, the mounting element comprises: a first mountingsubstrate, to which a first end of each electrode of the set ofelectrodes is attached; and a second mounting substrate, to which asecond end of each electrode of the set of electrodes is attached. Eachof the first and second mounting substrate may comprise (or be) arespective PCB. Preferably, the first mounting substrate comprises oneor more first electrical connections to every second electrode of theset of electrodes as spatially arranged. Then, the second mountingsubstrate may comprise one or more second electrical connections toelectrodes of the set of electrodes not connected to every secondelectrode of the set of electrodes between the electrodes connected tothe one or more first electrical connections. The second electricalconnections are beneficially arranged to provide an electrical powerthat is different from an electrical power provided by the firstelectrical connections, in particular an RF voltage of opposite phase tothat provided to the first electrical connections (as will be discussedbelow). Alternative designs will be discussed below.

With reference to FIGS. 3A, 3B, 3C and 3D, there are shown manufacturesteps for forming such an ion guide. In FIG. 3A, a single, elongatedplate electrode 40 is shown, having 5 apertures (as an example).Multiple plate electrodes 40 are formed into a stack, as shown in FIG.3B, and alignment of the apertures forms a plurality of individualchannels for ions to flow therethrough, with an example ion path 50being shown. Referring to FIG. 3C, the plate electrodes 40 are slightlyshifted axially with respect to each other (by less than the aperturespacing) so that the apertures overlap and the ion paths 50 are slanted.In FIG. 3D, the plate electrodes 40 are placed along a cylindrical axisof rotation, whilst maintaining the axial spacing or function. The axialshift in one rotation is made equal to the aperture spacing and as aresult, a single ion flight path 50 of a helical shape is formed, sincethe ion beam will switch at the end of each rotation to the nextaperture on the plate electrodes. This ion flight path 50 can form adrift region for ions, for an IMS configuration in particular.

At a conceptual level, the approach described in the foregoing providesan ion guide (with corresponding drift region) formed from a stack ofmounted electrode plates, each containing an array of apertures, wherethe last electrode meets the first. Through the application of an axialshift from one plate electrode 40 to the next, the paths through theapertures fuse into a single elongated ion path.

With reference to FIG. 4 , there is schematically depicted an operationof an ion guide in accordance with the design of FIG. 1 . Ions enter theion guide through inlet 52 and proceed along the helical ion path 50,exiting the ion guide at outlet 54. The axial shift of the plateelectrodes 40 (with reference to FIGS. 3C and 3D, for example) providesspace for the injection and extraction of ions to and from the helicaldrift region. Ions can be injected to the ion guide by aligning theoutput of another ion optical device to the inlet 52 and received fromthe ion guide by aligning the input of a further ion optical device tooutlet 54. If the spatial offset on the plate electrodes 40 is definedby the electrodes being mounted to a shaped component or spacer, theshape of that part is desirably configured to allow access to and fromthe channel.

Ions are constrained within the channel by applying different RF phasesto each adjacent plate electrode 40 (in other words, the phase of the RFapplied alternates between adjacent plate electrodes 40). If the plateelectrodes 40 are mounted between two PCB substrates (as shown in FIGS.1 and 2 , for instance), it is advantageous to apply RF voltages havingthe opposing phases to the different PCB substrates to minimisecapacitance effects. This is illustrated with reference to FIG. 5 ,which is a schematic diagram showing connections to and interfaces withsuch an ion guide 10. The plate electrodes 40 are mounted between firstPCB substrate 20 and second PCB substrate 30. A metal cover 60 isprovided to enclose the device, which is then mounted on a PEEK or metalmounting 70. Enclosing the ion flight path (drift region) allowsmaintaining it at a relatively elevated pressure compared with asurrounding vacuum of adjacent parts of the instrument. The pressure ofregion surrounding the metal cover 60 could be as low as 1×10⁻⁴ Pa(1×10⁻⁶ mbar) and as high as 200 Pa (2 mbar), although 1×10⁻³ Pa to 1 Pa(1×10⁻⁵ to 1×10⁻² mbar) is more typical. Within the ion guide (metalcover 60), a range of 0.01 to 1000 Pa (1×10⁻⁴ to 10 mbar) is possible,but likely optimised at or around 0.5 Pa (5×10⁻³ mbar). Ion mobilityitself works over a wide range, but the required voltages can becomedangerous if the pressure is too high.

An injection ion guide 80 is used to provide ions to the ion guide 10and an extraction guide 90 receives ions from the ion guide 10. Theinjection ion guide 80 is preceded by an ion source (that is, the ionsource is provided upstream from the injection ion guide 80). The ionsource may be any suitable known type, for example: an atmosphericpressure ion source, electrospray ion source, chemical ionisation ionsource, MALDI ion source, electron impact ion source, or laserionization ion source. Generally, the ion source is followed by an iontrap or other ion bunching device (which may be incorporated into theinjection ion guide 80 by applying appropriate stopping and extractionDC potentials). This can supply the drift region with tight packets(that is, pulses) of ions that can then be separated out by theirmobility within the drift region. An ion detector is provided after theextraction guide, or a further mass analyser for more complex analysis.

A RF potential of a first phase 25 is supplied to the first PCBsubstrate 20, which then has electrical connections to alternate plateelectrodes 40. A RF potential of a second, opposite phase 35 is suppliedto the second PCB substrate 30, which then has electrical connections tothe other plate electrodes 40, not connected to the first PCB substrate20.

Ions may be propelled through the flight path 50 by application of a DCtravelling wave to the first PCB substrate 20 and/or the second PCBsubstrate 30, which has electrical connections to the plate electrodes40. Specifically, DC potentials are superimposed onto the twoconstraining RF voltages of opposite phases. This is potentiallyachieved in the same manner using a travelling wave, as discussed in USPatent Publication No. 2011/0168882 or less preferably using transientDC potentials, as discussed in US Patent Publication 2014/0353487. Inthe design of FIGS. 1 to 5 , a single plate electrode 40 provides apotential for several points along the ion flight path 50. Consequently,it is difficult and not particularly practical to drive ions across witha constant DC gradient as would be conventional in existing IMS devices.As an alternative, an RF travelling wave may be created by applyingseveral RF phases to adjacent plates in the manner of an ion conveyer(such as discussed in U.S. Pat. No. 6,894,286 or 9,536,721).

These features may be understood with reference to the generalised termsused above. In that sense, there may additionally be provided a powersupply system configured to supply one or more voltages to the set ofplate electrodes, so as to confine ions to or within the continuous ionflight path and/or to cause ions to travel through the continuous ionflight path.

There may be provided an RF power supply, configured to provide eachelectrode of the set of electrodes with a respective RF voltage, suchthat adjacent electrodes receive RF voltages with different phases. Inparticular, the RF voltages may cause ions to be confined within thecontinuous ion flight path. In some embodiments, the RF power supply maybe further configured to provide each electrode of the set of electrodeswith a respective RF voltage so as to cause ions to travel through thedefined ion flight path. The RF power supply is preferably configured toprovide a first RF voltage to every second plate electrode of the set ofelectrodes as spatially arranged and to provide a second RF voltage toevery second plate electrode of the set of electrodes not receiving thefirst RF voltage. In particular, the first RF voltage generally hasopposite phase to the second RF voltage. Advantageously, the first andsecond RF voltages have the same amplitude and/or frequency.

In preferred embodiments, there is also provided a DC power supply,configured to supply at least one DC potential to one or more electrodesof the set of electrodes. The DC power supply is preferably configuredto provide DC voltages to at least some electrodes of the set ofelectrodes to form a travelling wave, so as to cause ions to travelthrough the defined ion flight path.

More specific details are now provided, in relation to the design shownin FIGS. 1 to 5 . A stacked ring ion guide, of the type shown morespecifically in FIG. 1 , will typically have plate electrodes 40 spacedevery 0.5 mm to 2 mm (the spacing could be uniform or variable), withplate electrode 40 having a thickness of between 0.25 mm and 1 mm(again, of uniform or differing thicknesses). Preferably, the plateelectrodes 40 would be spaced every millimetre and be 0.5 mm thick. Theplate electrodes 40 are typically metal, preferably made of steel oraluminium. Additionally or alternatively, the plate electrodes 40 may bepartially or fully coated with a metal such as gold, which can beespecially useful if the plate electrodes 40 are to be soldered to aPCB.

The apertures in the plate electrodes 40 may cover a wide variety ofshapes, including circular, oval, rectangular, rings or less regularshapes. It is generally preferable that the apertures be of a letterbox(rectangular or rounded rectangular) or ovoid shape extending down thelength of the ion guide. This may maximise the size of the aperture forspace charge capacity, but minimise the diffusion caused by differencesin the possible radii of the ion path. In this design, the apertureshapes are all the same. Alternative are discussed below, however.

The length and width of rectangular-shaped apertures may be anythingfrom 1 mm upwards. Aperture width is preferably kept small, generally toless than (or no more than) 5 mm, to limit the ion path lengthvariability. Larger widths are possible, especially if the radius of thehelix is large (for instance, a radius of at least or greater than 150mm). Aperture length may be limited by the available axial shift peradjacent aperture, which must itself be limited so as to maintain theintegrity of the ion guide. Large axial shifts between apertures ofadjacent plate electrodes 40 may cause transmission loss and iondiffusion. Generally, up to and around 100 μm of axial shift betweenapertures is considered safe, as this starts to approach the mechanicalaccuracy of the assembly, though perhaps considerably larger shifts aretolerable for rectangular apertures, for instance up to, around orslightly greater than 250 μm. The plate electrodes 40 are advantageouslyidentical to one another and in this case, inter-aperture distanceacross the plate should be constant.

An example of an ion guide in accordance with the design of FIG. 1 wouldform a helical drift tube comprising 180 plate electrodes 40, each ofwhich is 0.5 mm thick. The plate electrodes 40 are spaced every 1 mm(referenced to the centre of the apertures). This may give a compactcentral helical radius of 57.3 mm and 100 μm of axial shift betweenadjacent plate electrodes 40 allows a single turn of a helix to be up to18 mm long. There may some overheads between apertures of adjacent plateelectrodes 40, particularly for electrode material or to provide spacefor ion injection or extraction at the terminating ends. As aconsequence, 15 mm long apertures are feasible.

If such a helix extends over 11 turns to form a device having an axiallength of just below 20 cm (19.8 cm), the overall drift path (ion flightpath) would be almost 2 m. Doubling or tripling this scale in alldimensions is mechanically feasible within a bench-top instrument,giving path lengths of 16 m and 54 m respectively. Longer path lengthsthan these start to become unnecessary and may suffer from a law ofdiminishing returns, as ions diffuse over the path length (sinceresolution is proportional to square root of path length). One issue isthat very long thin electrode plates may start to sag, though thiseffect is averaged over many plates with each quarter turn andadditional central support could be applied if necessary. Gas pressurewithin the device, preferably filled with helium or nitrogen, isnormally around 0.1 mbar (10 Pa) to 1 mbar (100 Pa), although widevariations are possible.

An RF voltage of around 300V peak-to-peak as is suitable. Theapplication of RF voltages of opposing phases to adjacent plateelectrodes 40 means that the total number of plates is desirably an evennumber. If a travelling wave of transient DC pulses is applied, forexample where an approximately 10V pulse is applied to every fourthelectrode and that pulse is configured to “travel down” each series offour electrode plates, the total number of electrodes in a stack isdesirably divisible by 4.

In generalised terms as discussed above, each plate electrode of the setof plate electrodes may have one or more of the same: shape; size;positioning of apertures; and spacing of apertures. For each plateelectrode, the plurality of apertures are optionally all the same shape.The shape of the apertures may be same between plate electrodes, in someembodiments. Beneficially, each of the plurality of apertures of eachplate electrode has a rectangular or ovoid (oval) shape. Circular,rectangular, rings and other regular (such as polygonal) or irregularshapes are also possible. Other shapes of aperture and differencesbetween aperture shapes are discussed below.

With reference to FIG. 6 , there is schematically illustrated a massspectrometer 100 comprising an ion guide in accordance with thedisclosure. This comprises: an ion source 110; a S-lens 120; an inpution guide 130; a 90 degree ion guide 140; the ion guide 10 of FIGS. 1-5, as an ion mobility separator; a quadrupole mass filter 150; an outpution guide 160; a curved trap (C-trap) 170; a collision cell 180; and anorbital trapping mass analyser 190. In this example, the ion mobilityseparator 10 acts to separate out ions before the quadrupole mass filter150. This can then be used, for example, to: enhance the duty cycle ofthe quadrupole mass filter 150; remove chemical interferences; and/orgive mobility information for parent ions. In variations on thisarrangement, the ion mobility separator 10 may additionally oralternatively be located after the quadrupole mass filter 150, orbetween the collision cell 180 and the C-Trap 170 for mobilityseparation of fragment ions.

In another configuration, the collision cell 180 could be locatedupstream of the C-trap 170 but downstream of the mass filter 150 and theion mobility separator 10 could be located after the collision cell formobility separation of fragment ions. It will be appreciated that stillother configurations of mass spectrometer comprising an ion guide inaccordance with the disclosure are possible. In general, any suitableexisting configuration of mass spectrometer comprising an ion mobilityseparator may be constructed using the ion guide in accordance with thisdisclosure as the ion mobility separator.

It is noted that, even though such a system should be lossless inprinciple, elongated drift regions can have substantial ion losses. Forsensitivity and possibly for some fast hybrid instrument modes ofoperation, an option to bypass completely the ion mobility separator 10(with its elongated drift region) may be provided. Branched ion guides(such as discussed in US Patent Publication 2008/0061227) or traps (asconsidered in US Patent Publication 2014/0353487) connected via a shortion guide would be suitable for this purpose.

In generalised terms, an aspect of the disclosure may be considered as amass spectrometer, comprising any ion guide as herein disclosed.Advantageously, the ion guide is configured to receive ions from anupstream ion source or ion optical device and to cause the received ionsto travel along the ion flight path. The mass spectrometer may furthercomprise a mass analyser, configured to receive ions that have travelledalong the ion flight path and optionally, analyse the received ions. Insome embodiments, the mass spectrometer may further comprise an ionoptical bypass arrangement, configured selectively to cause ions totravel from the upstream ion source or ion optical device to the massanalyser without passing through the ion guide. This may comprise one ormore ion deflectors, for example.

It will be appreciated that variations to the foregoing design can bemade while still falling within the scope of the disclosure. Forexample, the axial shift of the aperture between adjacent plateelectrodes 40 does not need to be created by mounting plates between twohelically-shaped PCBs. A single helical board could be used and theother terminus could be a block cut from PEEK or ceramic, with slots cutin to position the plates and a suitable hole cut to allow access to theterminus.

With reference to FIG. 7A, there is depicted an example electrodestructure and mounting substrate according to a second design of an ionguide in accordance with the disclosure. In this alternative design, theaxial shift is entirely defined on flat PCBs 220 (or less preferably,additional metal or insulating parts), by providing the plate electrodes240 with a wedged shape at one or both termini. The mounting PCBs 220carry slots of varying length around the axis of rotation, such thatpenetration of the wedge into the slot varies in distance based on theslot width to control the axial position of the plates. Thereby, theplate electrodes 240 and thereby their respective apertures are providedwith the progressive axial shift around the axis of rotation. Slots canbe inexpensively laser-cut or milled into the PCB 220. The electrodeplates are thereby mounted (in a sandwich fashion) between the two flatPCBs 220.

Referring now to FIG. 7B, there is shown an electrode structure andmounting substrate according to a third design of an ion guide inaccordance with the disclosure. This comprises: two opposing PCBs 260;an offset-defining spacer 280; and plate electrodes 40. In thisalternative structure, the axial shift is defined by a function milledinto the spacer piece 280 at a terminus of the plate electrode set 40.As an alternative, but similar approach slots of varying depth may becut into the spacer. Such approaches allow positions of the plateelectrodes 40 to be defined by a part other that the PCB 280. In eitherdesign, electrical connections may be made by soldering to one or morePCBs 260 mounted onto or near the spacer 280. Advantageously, the PCBs280 can then be flat, with the connecting part of the plates penetratingthrough at various lengths.

PCBs are not strictly required, but useful as a means to delivervoltages. In one further design, electrical connections and to an extentmechanical definition and support may be made with metal rings withetched/cut connecting slots, or by direct wiring of the electrodeplates.

In various designs, the plate electrodes, each with a series ofelectrode apertures, may be formed of PCB or ceramic plates withmetallised apertures. A metallised PCB may benefit from reducedcapacitance, but may suffer risk of charging and electrical breakdownfrom sharp metal edges. Metal plates may be constructed to minimiseoverlapping metal regions with opposing RF. Additional grounded platesmay be placed between plate electrodes to which RF is applied, to shieldopposing RF voltages from one another.

In the generalised sense discussed above, the mounting element maycomprise a mounting substrate, to which each electrode of the set ofelectrodes is attached, the mounting substrate having a shape to therebyset the relative positioning of apertures between adjacent electrodes ofthe set of electrodes. Additionally or alternatively, the mountingelement may comprise: a mounting substrate; and a spacer, positionedbetween the mounting substrate and the set of electrodes. The spacer maybe configured to set the relative positioning of apertures betweenadjacent electrodes of the set of electrodes.

In a further alternative design, the plate electrodes may differ fromone another, which still achieving the same effect as the designdiscussed above. One way to implement this would be to create the axialoffset between apertures on adjacent plate electrodes by setting theaperture position on each plate electrode accordingly. This may greatlycomplicate manufacturing, but is still feasible. Care is desirably takento maintain access for ion injection and extraction.

As mentioned earlier, resolution may be limited by variation in pathlength caused by ions being able to sit on the outer or inner radius ofthe helical path. Space charge effects will magnify this problem byforcing ions out to the extremes and keeping them there. Although thedesigns discussed above result in helical ion flight paths with acircular two-dimensional profile (for example, when viewed from directlyabove or directly below), other two-dimensional profiles are possible.Referring now to FIGS. 8A and 8B, there are schematically shown variantprofiles for ion guides, in particular: (a) a rounded-rectangle (or“squared”) profile; and (b) a labyrinthine profile. Other closed shapesfor the two-dimensional profile could be envisaged. Two-dimensionalprofiles with a lower proportion of curvature than a circular profile,such as those shown in FIG. 8A, may help to mitigate this resolutionlimitation. Labyrinthine profiles may also more efficiently compress anion flight path into the available space. Such structures still definean ion flight path with a generally helical shape, even though the ionflight path is not strictly a helix. That is, the ion flight paths inFIGS. 8A and 8B still comprise a rotational path, which also extends ina direction perpendicular to the direction of rotation, as with a helix.

Another option to address the issue of limited resolution is use of afigure-of-eight profile, an example of which is discussed in US PatentPublication 2014/0042315, mentioned above. The approach described thereuses equal length regions of clockwise and anticlockwise curvature toequilibrate the path, for example allowing ions to spend equal time onouter and inner radii of the path, and thus compensate aberrations.Space charge effects may be helpful in this approach, as they preventions from migrating between different paths.

A difficulty with the embodiment of FIGS. 1 to 5 above is that it makesa figure-of-eight pattern difficult to implement, as ion paths ofopposing curvature cannot normally cross. Referring now to FIG. 9 ,there is depicted schematically an electrode structure and profile of afourth design of an ion guide, which addresses this issue. The righthand side shows the two-dimensional profile of the ion guide inaccordance with this design and the left-hand side illustrates thestructure of electrode plates at three different parts of thetwo-dimensional profile. Essentially, the figure-of-eighttwo-dimensional profile is formed using two helixes with circularprofiles that overlap, to allow ions to move between helixes after eachturn. The structure of electrode plates to allow this will be discussedbelow.

Starting with the top part of the two-dimensional profile, a firstelectrode plate structure 300 is shown. This electrode plate structureis no different from those shown in FIGS. 1, 3A to 3D and 5 , forinstance. In the middle of the two-dimensional profile, interleavingfirst 310 and second 320 electrode plate structures are shown. Theseelongated electrode plates have a serrated pattern, so that the first310 and second 320 electrode plates interleave. As a result, ionsfollowing the curvature of the top helix are passed to the bottom helixto travel with an opposing curvature at the end of each turn, withoutions come into conflict with one another. It will be recognised that thepassing of ions between the opposing curvature flight paths need nothappen after every turn, but preferably is caused to happen such thatthe ions travel the same distance through flight paths of both opposedcurvatures. Such a design can be beneficial, but is mechanicallycomplex.

In the general sense discussed above, it may be considered that thehelical or helical-based shape defines a two-dimensional profile. Then,the relative positioning of each plurality of apertures of a respectiveplate electrode of the set of plate electrodes and respective adjacentplate electrodes of the set of plate electrodes preferably defines thecontinuous ion flight path to extend multiple times along thetwo-dimensional profile. In other words, the continuous ion flight pathextends multiple turns around the helical-based shape.

The two-dimensional profile has, in one embodiment, a circular shape.Other closed-loop shapes are possible, such as oval, rounded rectangularor labyrinthine. In certain embodiments, the two-dimensional profile hasa figure-of-eight (lemniscate) shape. One way to implement such a designis for the set of plate electrodes to comprise first and secondpluralities of (plate) electrodes. Each of the first and secondpluralities of electrodes is arranged to define a respective circulartwo-dimensional profile. Some of the first plurality of electrodes andsome of the second plurality of electrodes are arranged to interleavewith one another, such that the two-dimensional profile of the firstplurality of electrodes overlaps with the two-dimensional profile of thesecond plurality of electrodes. Then, the continuous ion flight path isadvantageously defined by the plurality of apertures of both the firstand second pluralities of electrodes. For example, the interleavingelectrodes may have a serrated shape (typically with a square form). Theserration of the interleaving electrodes from the first plurality ofelectrodes is beneficially configured to mirror the serration of theinterleaving electrodes from the second plurality of electrodes, suchthat the electrodes can interleave. The apertures of the first pluralityof electrodes may thereby receive ions from the apertures of the secondplurality of electrodes and the apertures of the second plurality ofelectrodes may receive ions from the apertures of the first plurality ofelectrodes accordingly.

Further alternative structures can be considered. With reference to FIG.10A, there is shown a top view of a fifth design of an ion guide inaccordance with the disclosure. This depicts another type structure thatcan be efficiently built with multi-aperture electrodes as a “flatspiral”. In this design, adjacent plates need not be shifted relative toone another along the axis of rotation, along which the plate electrodesare arranged. Instead, the distance of the plate electrodes from therotational axis is shifted between successive plate electrodes. If theplates are arranged facing away from the axis of rotation this forms asingle spiral path for the ions, instead of a helical path.

In FIG. 10A, the multi-aperture electrodes 340 (shown here, each having5 apertures 341) are each shifted perpendicularly to the axis ofrotation (marked by dot 342 and extending into and out of the plane ofthe drawing). As shown in this drawing, ions would enter the structureat inlet port 350 and exit the structure at outlet port 360. They wouldtherefore travel along spiral-shaped ion flight path 365. This approachmay be combined with others disclosed herein, for instance the otherdescribed methods for equalisation of flight path for ions on the innerand outer radii may also be applied, as discussed below.

The axial offset can be implemented in the same manner as for thehelical structures, that is via bending of the support PCB (which wouldbe located at the outer edge of plate electrodes 340 and extend into theplane of the drawing), slots that define penetration of the electrodesinto the support or a spacer piece, or other suitable structure.

In the general terms as considered above, some or all of the set ofplate electrodes may be spatially arranged around an axis that isperpendicular to the first dimension (the dimension along which theplurality of apertures of each plate electrode are spaced). Then, thefirst dimension is typically radial to the axis and the continuous ionflight path has a spiral-based shape. A spiral-based shape may refer toa shape having a fundamental spiral character, for instance a curve witha generally increasing (or decreasing) radius from the axis. Inparticular, this may be achieved by each respective adjacent plateelectrodes of the set of plate electrodes being positioned so as to beoffset from one another in the first dimension (the radial dimension).Variants on a spiral shape (in which the spiral character is modulatedby some other shape, for example with a slight variation in a dimensionperpendicular to the direction of the spiral travel, to ‘zigzag’) canalso be considered.

Some helical character may be included by adding an axial shift inaddition to the radial, to allow: space for adjacent ion opticalcomponents; or space to switch the ion path from spiral to anti-spiralconfigurations (by reversing the radial shift trend). Thus, this maygreatly extend the path length within a small space, by stackingalternating spiral and anti-spiral structures. A structure in accordancewith this latter proposal is discussed with reference to FIGS. 10B, 10Cand 10D.

With reference to FIG. 10B, there is shown a top view of a first part ofa variant on the design of FIG. 10A and with reference to FIG. 10C thereis shown a top view of a second part of this variant design. The twoparts are stacked (in two levels) with the part shown in FIG. 10B onbottom (level 1) and the part shown in FIG. 10C on top (level 2). Ionsenter the structure through ion inlet 370 and pass through first plateelectrodes 374 to travel along first spiral ion flight path 375 (anoutward travelling spiral) and emerge through intermediate ion outlet378. These ions are then directed (potentially through furtherdeflection electrodes, not shown) to intermediate ion inlet 380 on thesecond level (FIG. 100 ). From here, the ions pass through second plateelectrodes 384 to travel along second spiral ion flight path 385 (aninward travelling spiral) and emerge through ion outlet 388. Electrodeplates may be constructed (for example etched) with two dimensions ofaperture stacking, such that multiple levels may be incorporated into asingle ring of electrode plates. Referring to FIG. 10D, there isschematically illustrated the ion flight path for the design of FIGS.10B and 10C, using the same reference numerals as those drawings toindicate the path of ions from ion inlet 370, through spiral ion flightregion 375 and opposing spiral ion flight region 385 to emerge at ionoutlet 388.

In general terms, each respective adjacent plate electrodes of the setof plate electrodes may be positioned so as to be offset from oneanother in the axial dimension. This can cause the continuous ion flightpath to have a shape that is both spiral-based and helical-based.

In embodiments, it may be considered that the set of plate electrodescomprises first and second pluralities of electrodes. The firstplurality of electrodes are typically spatially arranged such that arelative positioning of each plurality of apertures of a respectiveplate electrode of the first plurality of electrodes and respectiveadjacent plate electrodes of the first plurality of electrodes defines afirst continuous ion flight path through the respective plurality ofapertures of each plate electrode of the first plurality of electrodes.The second plurality of electrodes are generally spatially arranged suchthat a relative positioning of each plurality of apertures of arespective plate electrode of the second plurality of electrodes andrespective adjacent plate electrodes of the second plurality ofelectrodes defines a second continuous ion flight path through therespective plurality of apertures of each plate electrode of the secondplurality of electrodes. The second plurality of electrodes may bestacked on the first plurality of electrodes (for instance, with thefirst plurality of electrodes being generally arranged in a first planeand the second plurality of electrodes being arranged in a second planethat is parallel to the first plane but spaced from the first plane in adirection perpendicular to it), such that ions exiting the firstcontinuous ion flight path are directed onto the second continuous ionflight path. This is particularly advantageous where the first and/orsecond continuous ion flight paths have a spiral-based and helical basedshape.

For example, an entrance to the first continuous ion flight path may beprovided at a first end of one of the first plurality of electrodes andan exit from the first continuous ion flight path may be provided at asecond end of one of the first plurality of electrodes, opposite thefirst end (the first and second ends being defined in the firstdimension). Then, an entrance to the second continuous ion flight pathmay be provided at the second end of one of the second plurality ofelectrodes (aligned with the second end of the first plurality ofelectrodes) and an exit from the first continuous ion flight path may beprovided at the first end of one of the second plurality of electrodes(aligned with the first end of the first plurality of electrodes).

Optionally, the first plurality of electrodes is spatially arrangedaround a first axis (the first continuous ion flight path extendingalong a direction of the first axis) and the second plurality ofelectrodes is spatially arranged around a second axis (the secondcontinuous ion flight path extending along a direction of the secondaxis). Then, the first and second axes may be (substantially) parallelor (substantially) co-axial.

As mentioned previously, although it can be advantageous that each ofthe plate electrodes be identical, it is not necessary. A furtherbenefit in mitigating the resolution reduction can result from changingthe aperture shape between apertures of adjacent electrodes along theion flight path. This is explained with reference to FIG. 11A, in whichthere are illustrated first examples of electrode aperture shapes 400,410, 420, 430, 440, 450, 460, 470. By changing the shape of apertures insequence along the ion flight path (showing by the increasing referencenumerals), ions may be induced to follow a tight path around the outerand inner radius, at least once per turn of the main helix. This may beequivalent to stirring the trapped ion packets, so that they follow amore equal path length. This approach could potentially be applied toany ion mobility device with curvature and need not only be used withion guides as described previously (for example, having ahelically-shaped ion flight path). The force creating this effect may beapplied by variation in the shape of apertures as ions progress aroundeach curve or turn of the ion flight path. At a conceptual level, it maybe understood that the variation in the structure of the apertures issuch that entrained ions experience similar drift paths to one another,even if there is considerable variation in the inner and outer radius ofthe aperture stack.

The approach shown in FIG. 11A has two connected slots 405, 415 asapertures (though more such slots could be used, if desirable). Thus,for example, each of the apertures in the embodiments of plateelectrodes shown in FIGS. 1, 3A-D and 5, could be made to comprise thetwo slots. Nodules or vanes 406, 407 separating the slots appear to movearound and/or change shape as with increasing distance along the ionflight path, that is as progressively moving through apertures fromplate to plate, causing ions to migrate around the aperture. It is notnecessary for the nodules or vanes 406, 407 to separate the aperturescompletely, although this is shown for simplicity. Although the slots405, 415 and nodules or vanes 406, 407 are only shown for a firstelectrode 400, the corresponding parts in the other electrodes willimmediately be recognised. Thus, ions travelling along the ion flightpath are caused to shift in a direction perpendicular to the directionof the ion flight path. By shifting the ions in a perpendiculardirection, particularly at the one or more curved portions of the ionflight path, the ions may be caused to travel along different parts ofthe ion flight path cross-section, for example to rotate around theapertures and thereby define a helical shape with the direction of theion flight path being the axis of the helical shape.

FIG. 11A demonstrates this approach with an aperture formed of twolinked slots in a generally rectangular shape. Referring next to FIG.11B, there is shown further examples of electrode aperture shapes inaccordance with the disclosure, suitable for ion guides. As shown inthis drawing, the aperture could also be a ring shape 480 (shown in thisdrawing with a single vane 481, although more than one such vane ornodule could be used) that shifts rotationally between successiveelectrodes as shown by the arrow, just a wide slot 482 with forceapplied by rotation of the slot between electrodes arranged in asequence as shown by the arrows or a ring slot 484 with one or morepenetrating nodules 485 protruding from the aperture side that shift inaccordance with the (this is less preferable as ions could migratearound the slot by themselves resulting in diffusion).

Although this effect has been shown by changing the shape of aperturesalong the ion flight path length, it may alternatively be achieved byapplying a voltage on additional electrodes mounted between the RFapertures, for example.

In a second aspect of a generalised sense (which may be combined withother aspects as herein described), there may be considered an ion guidecomprising a plurality of electrodes. Each electrode comprises at leastone aperture, so as to define an ion flight path (through the apertures)having at least one curve, which may define an average radius ofcurvature. An aperture of a first electrode of the plurality ofelectrodes is adjacent to an aperture of a second electrode of theplurality of electrodes along the ion flight path. Then, the aperture ofthe second electrode has a shape, electrical potential, and/or positiondifferent from that of the aperture of the first electrode so as tocause ions travelling along the ion flight path to shift in a directionperpendicular to the direction of the ion flight path. By shifting theions in a perpendicular direction, particularly at the one or morecurved portions of the ion flight path, the ions may be caused to travelalong different parts of the ion flight path cross-section. Inparticular, the ions may not necessarily be forced towards an inside oroutside part of the curved portion. In a preferred embodiment, the ionsmay be caused to oscillate between inside the average radius ofcurvature and outside the average radius of curvature. Such approachesmay mitigate resolution limitations due to path length variations. Forinstance, a difference in flight path length between ions entering theion guide at a position inside the average radius of curvature and ionsentering the ion guide at a position outside the average radius ofcurvature may be corrected

To combine this with the first aspect, it may be considered (forexample) that the ion flight path has a spiral-based and/orhelical-based shape. Moreover, each electrode may have a plurality ofapertures. The electrodes may be a plate electrode or an electrodestructure that functionally mimics a plate electrode.

In this second aspect, the direction perpendicular to the direction ofthe continuous ion flight path is preferably defined by a helical (orhelical-based) shape, with the direction of the ion flight path being anaxis of the helical shape. By causing ions to “spiral” (that is in thiscontext, travel in a helical shape), the ions are effectively stirred.It should be noted that (especially in combination with the firstaspect), the ion flight path may itself have a spiral and/or helicalshape, such that the ions travel along a spiral-based and/orhelical-based shaped ion flight path, in a helical motion (which may betermed a further helical shape) perpendicular to that path.

In some embodiments, the aperture of the first electrode and theaperture of the second electrode each comprise a respective first slotand a respective second slot. Each first slot is advantageously distinctand/or separated from the respective second slot. Then, the first slotof the aperture of the second electrode advantageously has a shapeand/or position different from the first slot of the aperture of thefirst electrode so as to cause ions travelling along the ion flight pathto shift in a first direction perpendicular to the direction of the ionflight path. Additionally or alternatively, the second slot of theaperture of the second electrode has a shape and/or position differentfrom the second slot of the aperture of the first electrode so as tocause ions travelling along the ion flight path to shift in a seconddirection perpendicular to the direction of the ion flight path.

In one embodiment, each first slot and each second slot have a shapedefined by respective portions of the same rectangle (with each of thefirst and second slots optionally including at least one corner of therectangle). In embodiments, the aperture of the first electrode and/orthe aperture of the second electrode each comprise a ring shape (whichmay be circular, oval, rectangular or another annular form).

In some designs, the aperture of the first electrode and/or the apertureof the second electrode each further comprise one or more vanes ornodules protruding from a side of the respective aperture that shiftrotationally between the first and second electrodes. In other designs,the aperture of the first electrode and the aperture of the secondelectrode each comprise a wide or straight slot. Then, the slot mayshift rotationally between the first and second electrodes. Therotational shift of the vanes, nodules and/or slot may cause the ions toshift perpendicularly to the flight path direction.

Preferably, the first and second directions are the same. In otherwords, the relative positioning the first and second slots both causeions to be pushed in the same way. This is typically in a helicalmotion, as discussed above, such that the first direction is defined bya first further helical shape and the second direction is defined by asecond further helical shape. Then, the direction of the ion flight pathis preferably an axis of both the first and second further helicalshapes. The first and second further helical shapes may be the same.Optionally, the second direction may be different from the firstdirection, for example, if one of the first and second further helicalshapes being right-handed and the other being left handed (differentchirality).

As discussed above, electrode arrangements or structures may be employedthat are not strictly plate electrodes, but which have the samefunctional effect. One such structure is described with reference toFIG. 12 , in which a perspective view of a sixth design of an ion guideis shown. This uses stacked bar electrodes 510, 520, rather than plateelectrode apertures. The stacked bar electrodes 510, 520 can be seen asa stack of electrode arrangements, in which each arrangement comprisestwo parallel bar electrodes, with a respective gap therebetween (the gapbeing in a dimension orthogonal to a direction of elongation of the barelectrodes). A RF voltage with a first phase is applied to first barelectrodes 510 and a RF voltage with a second, opposite phase is appliedto second bar electrodes 520. Preferably, no DC voltages are applied tothe first bar electrodes 510 and second bar electrodes 520. In betweenthe RF bar electrodes 510 and the RF bar electrodes 520, furtherelectrodes 500 are provided with a DC voltage applied. No RF voltagesare advantageously applied to the further electrodes 500. The DCelectrodes 500 therefore interleave between successive RF bar electrodes510, 520. These DC electrodes 500 provide lateral focusing. In thisdesign, they are shown as plate electrodes, but they may equivalently beprovided using bar electrodes or wires held from above or below. The DCelectrodes 500 thus can be seen to provide parallel electrode parts(vertical parts in the figure), with a respective gap therebetween (theplane of the gap being generally parallel to and spatially separatedfrom the plane of the gap between the bar electrodes 510 and/or theplane of the gap between the bar electrodes 520), which are arrangedorthogonally (at right angles) with respect to the parallel RF barelectrodes 510, 520. The electrode parts of the DC electrodes 500 may beparts of the plate at the sides of the plate aperture, or may beparallel DC bars or wires. In this way, the ion flight path or channelis defined in one dimension by the stacked arrangements of parallel barelectrodes carrying alternating RF potentials, and in another(orthogonal) dimension by DC electrode parts (which may be barelectrodes or aperture sides within an elongated plate). The barelectrodes 510, 520 therefore traverse the circumference of the ionflight path cross-section (the effective ‘aperture’ created by theparallel RF bar electrodes 510, 520 together with the DC electrodes500).

A downside with this configuration as that the DC electrodes 500 comebetween the RF bar electrodes 510, 520, increasing the RF stackseparation. It has some advantages though, in that the DC parts 500 canshield the opposing RF potentials from one another, reducingcapacitance. The channel height in this arrangement can be widely variedusing the DC parts 500 alone and is not constrained by physicalrestrictions imposed by the RF electrodes 510, 520. This can be usefulwhere narrow channels are desirable (as high channels can createresolution losses). Moreover, the travelling wave DC voltage could beapplied using the DC parts 500 alone and not have to be mixed in with RFvoltages. Alternatively, the RF electrodes 510, 520 and DC components500 may be swapped.

A particular benefit of a structure as shown in FIG. 12 may be realisedwhen such a structure is employed in the construction of a spiral ionguide, for instance of the type discussed with reference to FIGS. 1 to 5. In such an implementation, two relatively long parallel RF (optionallyonly; that is supplied only with one or more RF potentials) barelectrodes may be used to create an elongated channel in a first plane.Then, a layer of orthogonal DC wires, bars or apertures are provided(mounted) in a second plane, separated from the first plane (andpreferably generally parallel to the first plane, at least in onedimension). The layer of DC (only; that is supplied only with one ormore DC potentials) electrodes divides the channel and defines the ionpath and/or number of turns in the spiral. Alternatively, (and in linewith the swapped arrangement discussed above), the relatively longparallel bar electrodes may be provided with DC (only; that is only oneor more DC potentials) and the layer of orthogonal wires, bars orapertures may be provided with RF (only; that is only one or more RFpotentials).

In a generalised sense, there may be considered an ion guide inaccordance with a third aspect. This ion guide comprises: a firstplurality of electrode arrangements, each electrode arrangementcomprising respective parallel bar electrodes, with a respective gaptherebetween; and a second plurality of electrode arrangements, eachelectrode arrangement comprising respective parallel electrode parts,with a respective gap therebetween. The parallel electrode parts of thesecond plurality of electrode arrangements are preferably arrangedorthogonally (at right angles) with respect to the parallel barelectrodes of the first plurality of electrode arrangements. Therespective gaps of the first plurality of electrode arrangements arealigned with the respective gaps of the second plurality of electrodearrangements to (effectively provide apertures that) allow ions totravel therethrough along a continuous path. The first and secondpluralities of electrode arrangements are advantageously arrangedalternately along the continuous path. The parallel bar electrodes ofthe first plurality of electrode arrangements and the parallel electrodeparts of the second plurality of electrode arrangements may effectivelymimic plate electrodes in a functional sense.

Preferably, each of the first plurality of electrode arrangements isprovided with an RF potential and in some embodiments only an RFpotential (that is, any potential or potentials supplied to eachelectrode have no DC component). Additionally or alternatively, each ofthe second plurality of electrode arrangements is provided with a DCpotential and more preferably only a DC potential (that is, anypotential or potentials supplied to each electrode have no RFcomponent). This may be reversed, such that each of the first pluralityof electrode arrangements is provided with a DC potential and morepreferably only a DC potential (that is, any potential or potentialssupplied to each electrode have no RF component). Additionally oralternatively in this case, each of the second plurality of electrodearrangements is provided with an RF potential and in some embodimentsonly an RF potential (that is, any potential or potentials supplied toeach electrode have no DC component). Optionally, successive electrodearrangements in the first plurality of electrode arrangements (or forthe reversed arrangement, in the second plurality of electrodearrangements) are provided with RF potentials of different (optionally,opposite) phase. The use of DC only electrodes may partially shield theRF electrodes (in particular, when successive electrodes are suppliedwith RF potentials of different phases), as discussed above. In someembodiments, each electrode arrangement of the second plurality ofelectrode arrangements comprises a respective (optionally, plate; inthis sense, a plate is meant and not a structure that mimics a plate)electrode having an aperture to provide the respective gap.

Although the invention has been described with reference to particulartypes of devices and applications (particularly mass spectrometersand/or ion mobility spectrometers) and the invention has particularadvantages in such case, as discussed herein, the invention may beapplied to other types of device and/or application. The specificmanufacturing details of the ion guide and associated uses, whilstpotentially advantageous (especially in view of known manufacturingconstraints and capabilities), may be varied significantly to arrive atdevices with similar or identical operation. Each feature disclosed inthis specification, unless stated otherwise, may be replaced byalternative features serving the same, equivalent or similar purpose.Thus, unless stated otherwise, each feature disclosed is one exampleonly of a generic series of equivalent or similar features.

As used herein, including in the claims, unless the context indicatesotherwise, singular forms of the terms herein are to be construed asincluding the plural form and vice versa. For instance, unless thecontext indicates otherwise, a singular reference herein including inthe claims, such as “a” or “an” (such as an analogue to digitalconvertor) means “one or more” (for instance, one or more analogue todigital convertor). Throughout the description and claims of thisdisclosure, the words “comprise”, “including”, “having” and “contain”and variations of the words, for example “comprising” and “comprises” orsimilar, mean “including but not limited to”, and are not intended to(and do not) exclude other components.

The use of any and all examples, or exemplary language (“for instance”,“such as”, “for example” and like language) provided herein, is intendedmerely to better illustrate the invention and does not indicate alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Any steps described in this specification may be performed in any orderor simultaneously unless stated or the context requires otherwise.

All of the aspects and/or features disclosed in this specification maybe combined in any combination, except combinations where at least someof such features and/or steps are mutually exclusive. As describedherein, there may be particular combinations of aspects that are offurther benefit, such the aspects of ion guides for use in massspectrometers and/or ion mobility spectrometers. In particular, thepreferred features of the invention are applicable to all aspects of theinvention and may be used in any combination. Likewise, featuresdescribed in non-essential combinations may be used separately (not incombination).

The invention claimed is:
 1. An ion guide, comprising: a first pluralityof electrode arrangements, each electrode arrangement comprisingrespective parallel bar electrodes, with a respective gap therebetween;and a second plurality of electrode arrangements, each electrodearrangement comprising respective parallel electrode parts, with arespective gap therebetween, the parallel electrode parts of the secondplurality of electrode arrangements being arranged orthogonally withrespect to the parallel bar electrodes of the first plurality ofelectrode arrangements, such that the respective gaps of the firstplurality of electrode arrangements are aligned with the respective gapsof the second plurality of electrode arrangements to allow ions totravel therethrough along a continuous path; wherein the first andsecond pluralities of electrode arrangements are arranged alternatelyalong the continuous path; and wherein each of the first plurality ofelectrode arrangements is provided with an RF potential and each of thesecond plurality of electrode arrangements is provided only with one ormore DC potentials or wherein each of the first plurality of electrodearrangements is provided with only one or more DC potentials and each ofthe second plurality of electrode arrangements is provided with an RFpotential.
 2. The ion guide of claim 1, wherein each electrodearrangement of the second plurality of electrode arrangements comprisesa respective electrode having an aperture to provide the respective gap.3. The ion guide of claim 1, wherein successive electrode arrangementsin the first plurality of electrode arrangements or in the secondplurality of electrode arrangements are provided with RF potentials ofdifferent phase.
 4. The ion guide of claim 1, wherein the respective gapbetween each electrode arrangement in the first plurality of electrodearrangements lies in a dimension orthogonal to a direction of elongationof the parallel bar electrodes.
 5. The ion guide of claim 1, wherein therespective parallel electrode parts in each electrode arrangement of thesecond plurality of electrode arrangements include parts of a plate atsides of a plate aperture, parallel bar electrodes, or wires.
 6. The ionguide of claim 1, wherein the respective gap between each electrodearrangement in the second plurality of electrode arrangements isarranged orthogonally with respect to the respective gap betweenparallel bar electrodes of the first plurality of electrodearrangements.
 7. The ion guide of claim 1, wherein the continuous pathtraveled by ions is defined in a first dimension by the first pluralityof stacked electrode arrangements and is defined in a second, orthogonaldimension by the second plurality of electrode arrangements.